I cannot seem to get any submenus to be enabled when using them with the Popup Button Object or any of the various popup statements. Using the same code to generate an actual menu bar item works just fine with all the submenu items fully enabled.
See this thread from 2020. The temporary workround I found then no longer works, as Jim predicted would happen. Submenus can be attached to menu-bar menus and to popup menus in the data sheet, but not to popup menus in general.